As accompanied with rapid development of various types of recording medium, information amount that can be generally handled has been dramatically increased. In the past, music, games, and the like used to be commercially available via a magnetic tape, a floppy Disk®, or a ROM (Read Only Memory), each of which stores several-megabyte information. In the present time, recording mediums such as a CD-R (Compact Disc Recordable) and a DVD (Digital Video Disc) each having a large storage volume allow for distribution of a wide variety of information.
Such a large storage volume in each of the recording mediums makes it technically possible to (i) add BGM (BackGround Music) to a simple photo album style still image content, or (ii) play back audio data simultaneously with display of an electronic book, an electronic document, a web document, or the like.
Handling of audio data in each of such electronic contents usually depends on a player for playing the content, despite the content creator's intension.
For example, Japanese Unexamined Patent Publication Tokukaisho 62-34356/1987 (published on Feb. 14, 1987) discloses a technique for realizing automatic long-time music playback without any user's operation. In the technique of this Patent citation, music playback continues in accordance with respective data of a plurality of disks by repeating playing back all the disks, until the user makes an instruction to finish the music playback. This makes it possible to keep on outputting the audio data without any user's operation.
Meanwhile, Japanese Unexamined Patent Publication Tokukai 2005-44409 (published on Feb. 17, 2005) discloses a technique for avoiding silence between audio data. In the technique of this Patent citation, when there is found continuity between songs to be played in a row, silence between the songs is eliminated, with the result that the songs are played continuously. This allows the user to enjoy listening with substantially no silence between songs.
Further, Japanese Unexamined Patent Publication Tokukai 2004-95100 (published on Mar. 25, 2004) discloses a technique concerning association between video data and audio data. The technique of this Patent citation promotes efficiency of an authoring operation for actually associating a sound with an image in playing back a video content in which the image and the sound are associated with each other. Further, in the technique, BGM is played back only during a set period of time. This makes it possible to prevent the audio data from being intermittently interrupted due to the video data, which is information changing rapidly.
Each of the Patent citations pays attention to a way of continuously playing back audio data, in order to solve their problems. However, each of the Patent citations does not take into consideration a difference between respective playback times of data, which are associated with each other and which have different data formats. The difference is caused due to the association between the data.
Consider a case of viewing (reading) text-based data such as an electronic document or an electronic book. In this case, speed of reading the text-based data differs depending on a person unlike a case of viewing video data or the like. Therefore, it is impossible to determine one playback time for both the text-based data and audio data associated with the text-based data. This arises two problems: (1) the playback of the audio data possibly ends before finishing reading the text-based data; and (2) the playback of the audio data possibly ends at a point where a creator of the content does not intend the playback to end.
The problem (1) can be avoided by playing back the set audio data again from its beginning. This is attained by a conventional technique. The problem (2) is further classified into two cases: (i) a case where the playback of the audio data stops at a “predictable point”; and (ii) a case where the playback thereof stops at an “unpredictable point”.
Consider a case where a scene, a state, or a file is changed at a predictable point in the conventional technique. In this case, the playback of the audio data is interrupted and then another audio is played back, but the end of a section of the content and the stop of the BGM correspond to each other for the user, so that the user does not really feel strange even if, e.g., the song played back after the interruption is the same as the song played back before the interruption.
On the other hand, consider a case where there are “unpredictable” sections in the prepared content file. Examples of the unpredictable sections include groups, files, paragraphs, and the like. These unpredictable sections are unrecognizable while viewing the product content. Now, assume that BGM is set for each of the sections. In this case, the BGM is temporarily stopped being played back and then played back again (hereinafter, also referred to as “stop/playback process”) in the aforementioned conventional manner for every section unrecognizable for the user, so that the BGM is interrupted at a point unpredictable for the user and then is played back again. The user feels strange because he/she thinks that the BGM would have been continuously played back.
The following explains this problem more in detail, with reference to FIG. 11. FIG. 11 is an explanatory diagram illustrating such discontinuous BGM playback occurring in the conventional technique. See a portion indicated by a reference numeral 110 in FIG. 11. A display device 112 displays a page image 113 while BGM 115 is played back from a speaker (not shown).
Here, consider a case where the user instructs the display device 112 to switch display pages from the page image 113 to a page image 114. In response to the instruction, the display device switches the display pages from the page image 113 to the page image 114, and the playback of the BGM 115 from the speaker 15 is temporarily stopped. When the page image 114 is displayed by the display device 112, the BGM 115 is played back again. As such, upon switching the display images from the page image 113 to the page image 114, the BGM 115 is played back discontinuously.
As the user views (reads) faster, it takes shorter time for the user to reach each of the unpredictable sections, with the result that the user encounters the unpredictable sections so often. If the stop/playback process is carried out for every section in this case, a period of actually playing back the BGM becomes extremely short. As a result, it is almost impossible to obtain an effect as BGM.